1. Field of Invention
This invention relates to fastener driving devices and, more particularly, to fastener driving devices of the portable type having a self-sealing diaphragm valve.
2. Discussion of Related Art
Fastener driving tools for driving fasteners such as nails, staples or the like are commonly used in industry and commerce. The fasteners are generally supplied from a collated strip of fasteners disposed in a magazine coupled to a nosepiece portion of the fastener driving tool. The fastener driving tool also comprises a housing to store compressed air, a cylinder within the housing, a piston within the cylinder, a driver connected to the piston, and a main valve to provide pressurized air to operate the piston. Fastener driving tools also include a work contacting element coupled to a tool controlling mechanism operable as a safety feature to enable and disable the fastener driving tool. In some instances, this work contacting element is coupled with a depth adjusting mechanism that allows control and adjustment of the depth at which the fastener is driven into a work piece.
During operation of such tools, the tool is positioned in contact with a workpiece, such as wood or drywall, in such a manner as to allow the contacting element or the depth adjusting mechanism to be in direct contact with the work piece. The trigger is manually pulled to actuate a trigger valve which in turn operates the main valve that provides compressed air to move the piston. The trigger can also be made to be remotely controllable if desired.
Most tools utilize O-rings as seals, but they require proper lubrication to provide long wear life. Other arrangements have been tried such as that disclosed in U.S. Pat. No. 4,747,338. The firing valve disclosed in U.S. Pat. No. 4,747,338 is configured that exposure of multiple differential areas of the valve to a common high pressure results in the valve being biased toward a sealed position relative to the cylinder of tool while in the unfired position. The valve includes two rolling diaphragm seals.
U.S. Pat. No. 4,610,381 is directed to a drywall tool for driving a fastener with frequent multiple blows including a firing valve having first, second and third pressure zones. A movable O-ring seals the first pressure zone from a vent, a second movable seal seals the first pressure zone from the second pressure zone, and a rolling diaphragm seals the second pressure zone from the third pressure zone. The rolling diaphragm permanently seals the second pressure zone from the third pressure zone.
U.S. Pat. No. 5,207,143 is directed to a pneumatic fastener driving device having a trigger valve with flexible membrane that controls the flow of compressed air to and from the cylinder. The flexible membrane maintains the main valve close no matter when the tool is connected or disconnected to an air supply line. The flexible membrane extends between the housing and the main valve and is substantially supported by surfaces of the housing during movement.
All the prior art is limited in its performance by one or more of the following: requiring more parts to achieve the main valve as well as more intricate mechanisms to open and close the valve.
Therefore, it is desirable to overcome these and other limitations thus allowing overall improved performance and reduced cost of the fastener tool.